Although cognitive impairment is a common, distressing side effect of adjuvant chemotherapy for breast cancer, the fundamental brain mechanisms have not been systematically examined. Previous research suggests that cognitive alterations in women treated for breast cancer may be related to basic cognitive processes, attention and working memory, that are prerequisites for effective functioning in daily life. Thus, the specific aims are to determine: (1) whether functional alterations occur in neural brain activation patterns on functional magnetic resonance imaging (fMRI) testing of attention and working memory and in cognitive performance in women treated with adjuvant chemotherapy for breast cancer over time;(2) whether systematic functional changes in neural brain activation patterns observed on fMRI testing of attention and working memory are associated with changes in objective and subjective indicators of cognitive functioning over time. A longitudinal study will be conducted with 105 women, including 70 patients newly diagnosed with Stage I or II breast cancer treated with adjuvant chemotherapy (n = 35) or without chemotherapy (n = 35), and 35 women as healthy controls. Three repeated measures will be obtained to evaluate acute and longer-term effects of adjuvant chemotherapy on attention and working memory over a one-year interval: pre-chemotherapy;one month post- chemotherapy;and seven months post-chemotherapy to permit optimal recovery from treatment. An established attention and verbal working memory task will be used during fMRI testing. The event- related fMRI analysis will evaluate neural function in brain regions underlying attention and working memory based on research and implicated in preliminary findings. Neuropsychological test performance and self-report assessments will be used to test hypothesized associations with brain activation patterns on fMRI testing. Covariates of age, education, psychological state, physical symptom distress, and selected biological functional indicators will be assessed and controlled. The study will provide new information about the role of basic processes of attention and working memory in the emergence of cognitive side effects of adjuvant chemotherapy for breast cancer and will establish a foundation for targeted interventions to improve cognitive functioning in breast cancer survivors.